Since Richard R. Schrock and Robert H. Grubbs prepared two kinds of metathesis catalysts with transition metal carbene structure in the 1990's, it has been drawn extensive attention in the development of more active and selective ruthenium catalysts for different kinds of olefin metathesis reactions, e.g., ring-opening metathesis polymerization (ROMP), ring-closing metathesis (RCM), and cross metathesis (CM).
So far, some ruthenium complexes have been reported as active metathesis catalysts (1a-1b and 2a-2f in Scheme 1) for RCM and ROMP reactions (References for listed catalysts in Scheme 1; 1a: Grubbs et al., J. Am. Chem. Soc. 1992, 114, 3974-3975; 1b: Grubbs et al., Org. Lett 1999, 1, 953-956; 2a: Hoveyda et al., J. Am. Chem. Soc. 1999, 121, 791-799 and WO200214376A2; 2b: Zhan et al., US20070043180A1 and WO 2007003135A1; 2c: Tupy et al., WO2007081987A2; 2d: Slugovc et al., Organometallics 2004, 23(15), 3623-3626; 2e: Slugovc et al., Organometallics 2005, 24(10), 2255-2258; 2f: Grela et al., WO2004035596A1). However, a disadvantage of all reported ruthenium catalysts is obviously substrate-dependent for different kinds of ruthenium catalysts in metathesis reactions, and it is still very difficult to find some active metathesis catalysts selective for RCM and ROMP reactions, respectively. Moreover, only a few metathesis catalysts such as Grubbs catalyst 1b could be used effectively to make high-strength and high-stiffness polydicyclopentadiene (PDCPD) material by ROMP reaction.

Scheme 1: Structure of Some Ru Catalysts for ROMP and RCM Reaction
Currently, ROMP reaction is broadly used for preparation of various high-strength and other functional polymers. To overcome the activity and selectivity problems for ROMP catalysts, it has become a goal to develop more active and selective metathesis catalysts as an alternative for ROMP and RCM reactions, especially in ROMP for effective preparation and modification of different functional polymer materials. It is significantly important to develop more active and selective ruthenium catalyst for ROMP reactions with different kinds of olefin substrates to prepare highly functional polymer materials and also to improve polymer properties.